Comment on K. Michaelian and A. Simeonov (2015) “Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum”

This is a comment on: “Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum” by K. Michaelian and A. Simeonov, Biogeosciences, 12, 4913–4937, 2015. Michaelian and Simeonov formulate the leading thought in their article “The driving 10 force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate”. I doubt that the reasoning that follows regarding the role of “pigments” (in which they include all substances able to absorb solar radiation) is correct.

Early phototrophic organisms are thought to have evolved in water, and we shall deal with this later below, but start with the situation on land. Let us compare the optical properties of ground with and without vegetation, and those of of the Moon 30 with those of the terrestrial biosphere (by "terrestrial" we here mean not only "on planet Earth", but specifically "the part on land").
When you look at the Moon you will see brighter areas ("highlands") and darker areas ("mare"). Figure 1 (courtesy E. Foote Smith) shows what the materials in these two kinds of lunar surface look like close-up. As expected, the mare soil is darker 35 than the highland soil, but the highland soil probably does not look as white as expected. Remember that when we look at the Moon at night it is against a background of a dark sky, and our eyes are dark-adapted. We are fooled by the great contrast.
And the surface of the moon is not more reflecting than plant leaves ( Figure 2).

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Vegetation does not always look darker than ground without vegetation ( Figure 3). What is important in the context of what we are dealing with here is of course not what things look like. We must extend our interest into the infrared, a spectral region to which much of the solar radiation belongs (the ultraviolet is of less interest in this context). And the quantity we should consider as far as data are available is the hemispherical reflectance, not reflectance in a single direction.

The temporal aspect
We can also put a temporal aspect on this. If sunlight is absorbed by dead matter, it is usually converted to heat and 50 reradiated as heat radiation of ambient temperature within a short time. If it is absorbed by a photosynthetic system, much of the energy is retained for a long time, before eventually it is radiated as heat radiation, sometimes after having been processed through several steps in the food chain. Thus, the living system delays entropy increase. Some trees that had collected solar energy sank into swamps more than two hundred fifty million years ago, and their reduced carbon was preserved until the present era, when mankind started to burn coal and thereby generate entropy. Thus, entropy production 55 was delayed, i.e. the rate of production decreased, thanks to the chlorophyll and the photosynthesis of ancient trees that have been preserved as coal. The production and usage of oil is a similar phenomenon. We cannot back from our responsibility for our planet by claiming that we must burn all the coal and oil due to a "thermodynamic imperative".

The aquatic environment
Almost half the land area in Figure 6 looks quite dark. This area is covered by coniferous forest, mainly Scots pine (Pinus sylvestris) with some spruce (Picea abies). We must not be misled by the dark appearance; the reflectance is higher from 700 to 1300 nm (a substantial part of the solar spectrum, c.f. There are some small quite bright areas on the land surface. These bright areas consist of bare carbonate rock, also a result of (past) life. Another circumstance, not visible in Figure 6, is that forests have a tendency to increase cloudiness, and thereby 70 cause increased reflectance by the atmosphere (e.g., Teuling et al. 2017), and thereby counteract entropy increase.
I do not have available spectral curves from the sea shown in Figure 6, but turn to analogous situations described by Qi et al. (2020). They have published numerous reflection difference spectra for various lakes and ocean surfaces where algae are abundant, i.e. spectra that show the difference in reflectivity for water with and without algae. A sample is reproduced in Fig.   75 7.
The presence of algae increases the reflectivity of oceans and lakes, i.e. counteracts the "degradation" of sunlight to diffuse radiation of longer wavelength, and thus the production of radiation entropy.

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As far as we know there is no life on Mars; nevertheless the reflectivity (albedo) is very low even in brighter areas like Syrtis Major, although during dust storms, the albedo increases (Vincendon et al. 2015). The low reflectivity holds particularly for short wavelength (422 nm), but even red rocks reflect less than 10% of incident 733 nm and 1009 nm radiation over most angles (Johnson et al. 2021).

6 Conclusion
Michaelian & Simeneov (2015) conclude that they have presented evidence that "supports the thermodynamic dissipation theory of the origin of life (Michaelian, 2009(Michaelian, , 2011, which states that life arose and proliferated to carry out the thermodynamic function of dissipating the entropically most important part of the solar spectrum (the shortest wavelength photons) prevailing at Earth's surface and that this irreversible process began to evolve and couple with other irreversible 90 abiotic processes, such as the water cycle, to become more efficient, to cover ever more completely the electromagnetic spectrum, and to cover ever more of Earth's surface." I cannot agree that they have presented evidence for this conclusion. The biosphere has certainly evolved and is maintained thanks to a production of entropy associated with the conversion of solar radiation to Earth radiation. For details of this entropy production, I refer to Wu and Liu (2010). They compared and discussed various ways of computing entropy fluxes in the Earth system. 7 There are no competing interests 100 8 Acknowledgements Thanks are due to Beth Middleton for comments and language correction, and to Emily Foote Smith for Fig. 1.